Why
Slate Roofs Don't Need
Ice and Water Membrane

Traditional roofing
techniques have almost become extinct in the United States,
fading away with the passing generations of roofing craftsmen
over the decades. The generation gap between the traditional
roofers of the past and the modern roofers
of today has created a knowledge gap that at times seems
almost unbridgable. This is starkly evident when the issue
of ice and water membrane is raised.

At the International
Preservation Trades Workshops near Washington DC a couple
of years ago, during one of my Slate Roof Restoration presentations,
a roofing contractor in the audience raised his hand to
ask a question. When do you use ice and water membrane
on a slate roof? he asked.

Read my lips, I replied. N-E-V-E-R.

The contractor stood staring at me in silence, jaw agape,
dumfounded.

Weeks later I received a call from a roof restoration professional
and consultant in New England. She wanted to know why
I had included no ice and water membrane in the specs
on a 52 square re-roof with slate on a residential job
in Connecticut. During the process of answering her question,
she became so flabbergasted that she hung up on me. She
did not like hearing what I had to say. So hang on to
your seat  if youre an ice membrane
junkie, as so many modern roofers and architects today
are, youre in for a surprise.

There is a photo of a 150
year old slate roof in this site. This is a roof still
in good functioning condition. Does it have ice
membrane on it? No. There are millions of very old roofs
in the United States and around the world, roofs 100 years
old and some much older, still in good working order. Did
they need or ever use ice and water membrane? No. These are
traditional roofs constructed of traditional roofing methods.
They do not, nor did they ever need ice and water membrane.
Furthermore, these roofs can be duplicated today in the same
style and perform with the same longevity without a square
inch of ice and water membrane. So why do modern roofers
and architects now think that ice and water membrane should
be an essential part of every roof, as many seem to believe?

Well, aside from the roofing industrys heavy ice and
water membrane advertising pressure, we need to look at the
evolution of roof design to get to the bottom of this. A
generation or two ago, homeowners, architects, and roofers
looking for cheaper, faster roofing methods began to use
plywood for roof decks, covered with asphalt shingles. About
15 years into this modern development, roofers were shocked
to discover that the plywood decking was delaminating along
the bottom three feet of the roof, near the eaves. This was
due to several reasons: low-slope roofs with slow water and
snow run-off enabled ice and moisture to collect along the
eaves; the plywood was susceptible to glue failure under
hot, damp, and freeze-thaw conditions; and the roofs were
afflicted with poor roof ventilation or a lack of breathing due
to the plywood/asphalt combination smothering the roof and
preventing airflow. Guess what came to save the day? You
guessed it  ice and water membrane became employed
to prevent delamination of the plywood roof decks  a
band-aid solution to an inferior roof design. Inferior, that
is, to traditional roofs.

Todays modern roofers have become so steeped in the
plywood/asphalt roofing systems that they have also become
addicted to ice and water membrane, afraid to even think
about installing a roof without it. However, traditional
roofers who use traditional roofing methods avoid the use
of laminated roof decking materials and instead use natural
wood boards or lath. They avoid non-breathing roof coverings
and instead use natural slate or tile. Natural slate or ceramic
tile combined with a natural wood board deck is a breathable
roof. It is also a roof that does not need any ice and water
membrane nor does it benefit from it. This may not be the
sort of information that ice and water membrane manufacturers
want you to hear, but its information that many roofers
and architects need to know and understand. If you want to
air your opinion on this matter, visit the slate roofing message
board atSlateRoofCentral.com and lets
hear what you have to say.

[Author's postscript: It should
also be noted that peel and stick underlayments, and
virtually all underlayments have a very short life expectancy
relative to stone roofing. The idea that such underlayments
will benefit a slate roof over the life of the roof is
just incorrect. The underlayment will dry out, crack,
disintegrate, turn to dust and fail long before the roof
itself has reached its end. For
some reason, this is a hard concept for many in the roofing
and design industries to understand. If the underlayment
material will fail long before the roofing fails, and the
roofing will continue to service the building as a water-tight
barrier for decades despite the lack of effective underlayment,
then that should be seen as abundant proof that the underlayment's
purpose is to keep the water out of the building until
the final roofing is installed. Of course, this is assuming
the slate
roof is installed correctly with adequate headlaps,
sidelaps, slope, and flashings. If the installation is poor,
then the peel and stick underlayment may hide leaks long
enough for the contractor to get paid and disappear. At the
risk of being too candid, I must say that this may be a
big reason why peel and stick underlayments are so popular
today.]

Additional postscript: Ice membrane contains carcinogenic materials, which may be as much as 25%, according to the manufacturer's Material Safety Data Sheet.Read more about this.